This invention relates to wiper systems of modern motor vehicles in which different modes of operation can be chosen via an operating switch, as for instance continuous operation, intermittent operation, wipe-wash-operation. For implementing these different modes of operation a control device with a circuit is needed, which circuit releases time-dependent switching and/or controlling signals. A time-dependent switching signal, for example, determines the interval of the intermittent operation, another time-dependent switching signal could determine the wipe-after-wash period during the wipe-wash operation. In general, the time taken by such a switching signal is to be as constant as possible and does not depend on any conditions of environment.
Wiper systems, in which the wiper motor is switched off, if the wiper should be blocked outside its parking position and thus does not reach its parking position within a predetermined period of time, are known. In order to implement this anti-blocking protection, time-dependent controlling signals are needed, which are generated in the circuit. As known from experience, it is problematic to determine the period of time needed for controlling signals in this application because the period of time of a wiping cycle depends on influences of environment. Experiments made with wiper system, in which all time-dependent switching and controlling signals were derived from a timing signal with highly constant frequency have not always satisfactorily been successful.
Thus the object of the present invention is to provide a wiper system by using easiest means, which wiper system works in an optimal and safe manner during all modes of operation.